staging: sm7xxfb: rename smtc_screen_info to smtc_scr_info

This change of name improves readability on sm712_vga_setup and
smtcfb_pci_probe. It is coherent with the name of vars being used on
code while avoiding the use of extra long lines in functions.

Tested with SM712.

Signed-off-by: Javier M. Mellid <jmunhoz@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>