EDAC: Fixup scrubrate manipulation

Make the ->{get|set}_sdram_scrub_rate return the actual scrub rate
bandwidth it succeeded setting and remove superfluous arg pointer used
for that. A negative value returned still means that an error occurred
while setting the scrubrate. Document this for future reference.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>

diff --cc drivers/edac/amd64_edac.c
Simple merge

diff --cc drivers/edac/amd64_edac.h
Simple merge

diff --cc drivers/edac/cpc925_edac.c
Simple merge

diff --cc drivers/edac/e752x_edac.c
Simple merge

diff --cc drivers/edac/edac_core.h
Simple merge

diff --cc drivers/edac/edac_mc_sysfs.c
Simple merge

diff --cc drivers/edac/i5100_edac.c
Simple merge