staging: rtl8723bs: remove unused variable 'start' in hal/sdio_halinit.c

staging: rtl8723bs: remove unused variable 'start' in hal/sdio_halinit.c

fix following W=1 compiler issue:

drivers/staging/rtl8723bs/hal/sdio_halinit.c:
	In function '_ReadAdapterInfo8723BS':
drivers/staging/rtl8723bs/hal/sdio_halinit.c:1156:16:
warning: variable 'start' set but not used [-Wunused-but-set-variable]
1156 |  unsigned long start;
     |                ^~~~~

Signed-off-by: Fabio Aiuto <fabioaiuto83@gmail.com>
Link: https://lore.kernel.org/r/ce1faa15052b519738656e11658dee93f9e91c29.1618145345.git.fabioaiuto83@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>