padata: update documentation file path in MAINTAINERS

It's changed since the recent RST conversion.

Fixes: bfcdcef8c8 ("padata: update documentation")
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

MAINTAINERS

@@ -12426,7 +12426,7 @@ L:	linux-crypto@vger.kernel.org
 S:	Maintained
 F:	kernel/padata.c
 F:	include/linux/padata.h
-F:	Documentation/padata.txt
+F:	Documentation/core-api/padata.rst
 
 PAGE POOL
 M:	Jesper Dangaard Brouer <hawk@kernel.org>