staging: rtl8723bs: Fix compilation errors for W=1 build

staging: rtl8723bs: Fix compilation errors for W=1 build

When building a kernel with Clang 19 the couple of warnings
become the errors (due to CONFIG_WERROR=y by default).

.../rtl8723bs/core/rtw_xmit.c:1939:13: error: variable 'drop_cnt' set but not used [-Werror,-Wunused-but-set-variable]
.../rtl8723bs/hal/hal_com.c:893:6: error: variable 'res' set but not used [-Werror,-Wunused-but-set-variable]

Fix them accordingly.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20250415091019.545905-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>