staging: rtl8712: fix checkpatch warnings

This patch fixes multiline dereference warnings in
rtl871x_xmit.c:

WARNING: Avoid multiple line dereference - prefer 'psecuritypriv->XGrptxmickey'
379: FILE: drivers/staging//rtl8712/rtl871x_xmit.c:379:
+					psecuritypriv->
+					XGrptxmickey[psecuritypriv->

WARNING: Avoid multiple line dereference - prefer 'psecuritypriv->XGrpKeyid'
380: FILE: drivers/staging//rtl8712/rtl871x_xmit.c:380:
+					XGrptxmickey[psecuritypriv->
+					XGrpKeyid].skey);

Signed-off-by: Aiman Najjar <aiman.najjar@hurranet.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/ddd296c34c5b0206dfe5cf2e6cbe40e0a118c257.1585508171.git.aiman.najjar@hurranet.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>