video: fbdev: pmagb-b-fb: Remove bad `__init' annotation

Fix:

WARNING: drivers/video/fbdev/pmagb-b-fb.o(.text+0x6dc): Section mismatch in reference from the function pmagbbfb_probe() to the function .init.text:pmagbbfb_erase_cursor()
The function pmagbbfb_probe() 
references the function __init pmagbbfb_erase_cursor().
This is often because pmagbbfb_probe lacks a __init
annotation or the annotation of pmagbbfb_erase_cursor is wrong.

-- a fallout from a missed update from commit 5b1638d9 ("VIDEO: 
PMAGB-B: Fix section mismatch") and then commit 48c68c4f ("Drivers: 
video: remove __dev* attributes.")

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>