MAINTAINERS: add "hw/registerfields.h" in Register API entry

Orphan since afb3141c660

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
diff --git a/MAINTAINERS b/MAINTAINERS
index 45e2e20..55e4038 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1538,6 +1538,7 @@
 S: Maintained
 F: hw/core/register.c
 F: include/hw/register.h
+F: include/hw/registerfields.h
 
 SLIRP
 M: Samuel Thibault <samuel.thibault@ens-lyon.org>