EDAC: Handle empty msg strings when reporting errors

A reported error could look like this

[  226.178315] EDAC MC0: 1 CE  on mc#0csrow#0channel#0 (csrow:0 channel:0 page:0x427c0d offset:0xde0 grain:0 syndrome:0x1c6)

with two spaces back-to-back due to the msg argument of
edac_mc_handle_error being passed on empty by the specific drivers.
Handle that.

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