bes2600: thread struct device * through factory request_firmware() call

Follow-up to \"bes2600: use request_firmware() for factory.txt read\".
That patch switched the factory calibration read path from filp_open()
+ kernel_read() to request_firmware(), but passed dev=NULL to
request_firmware() because factory_section_read_file() did not have a
struct device * in scope. The resulting logs carry the
'(NULL device *):' prefix and do not propagate a udev association.

Add a module-local static struct device * used as the firmware-class
load context, plus a small exported setter:

    static struct device *bes2600_factory_dev;
    void bes2600_factory_set_dev(struct device *dev);

Wire bes2600_factory_set_dev(&func->dev) from bes2600_sdio_probe(),
right after bes2600_platform_data_init() so the platform layer has
already had a chance to use the same struct device for its own
initialization.

factory_section_read_file() now passes bes2600_factory_dev (instead
of NULL) to request_firmware(). When the factory read happens before
probe (not currently the case on PineTab2) the pointer is still NULL
and request_firmware() accepts that; no regression.

No API changes to bes2600_get_factory_cali_data() callers. The
char *path parameter remains (it is the firmware-class name fed
straight to request_firmware()).

Tested-on: PineTab2 (BES2600WM + RK3566) running linux-pinetab2
6.19.10-danctnix1-1. Driver probes, factory data is read, and any
post-c5 factory diagnostics now carry the SDIO device identity
instead of '(NULL device *)'.

Signed-off-by: Markus Fritsche <fritsche.markus@gmail.com>

bes2600/bes2600_factory.h

@@ -199,6 +199,9 @@ enum factory_cali_status {
 /* just calibrate 11n, other protocols are automatically mapped */
 #define WIFI_RF_11N_MODE 0x15
 
+/* set the struct device * used for request_firmware() context */
+void bes2600_factory_set_dev(struct device *dev);
+
 /* read wifi & bt factory cali value*/
 u8* bes2600_get_factory_cali_data(u8 *file_buffer, u32 *data_len, char *path);
 void factory_little_endian_cvrt(u8 *data);