staging: rtl8192e: rename FragNum to frag_num in sequence_control union

Fixes a checkpatch CHECK message.
Signed-off-by: William Durand <will+git@drnd.me>
Link: https://lore.kernel.org/r/20210214140332.16175-3-will+git@drnd.meSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192e/rtl819x_BA.h

@@ -22,7 +22,7 @@
 union sequence_control {
 	u16 short_data;
 	struct {
-		u16	FragNum:4;
+		u16	frag_num:4;
 		u16	SeqNum:12;
 	} field;
 };