MAINTAINERS: Remove sifive_l2_cache.c from EDAC-SIFIVE pattern

Commit

  9209fb51 ("riscv: move sifive_l2_cache.c to drivers/soc")

moved	arch/riscv/mm/sifive_l2_cache.c
to 	drivers/soc/sifive/sifive_l2_cache.c

and adjusted the MAINTAINERS EDAC-SIFIVE entry but slipped in a mistake.

Since then, ./scripts/get_maintainer.pl --self-test complains:

  warning: no file matches F: drivers/soc/sifive_l2_cache.c

Boris suggested that sifive_l2_cache.c is considered part of the SIFIVE
DRIVERS, not part of EDAC-SIFIVE. So simply drop this entry, and by the
sifive keyword pattern in SIFIVE PATTERNS, it is automatically part of
the SIFIVE DRIVERS.

Suggested-by: Borislav Petkov <bp@alien8.de>
Co-developed-by: Sebastian Duda <sebastian.duda@fau.de>
Signed-off-by: Sebastian Duda <sebastian.duda@fau.de>
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200413115255.7100-1-lukas.bulwahn@gmail.com