cramfs: better MTD dependency expression

Commit b9f5fb18 ("cramfs: fix MTD dependency") did what it says.

Since commit 9059a349 ("kconfig: fix relational operators for bool
and tristate symbols") it is possible to do it slightly better though.
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/cramfs/Kconfig

@@ -33,8 +33,7 @@ config CRAMFS_BLOCKDEV
 
 config CRAMFS_MTD
 	bool "Support CramFs image directly mapped in physical memory"
-	depends on CRAMFS && MTD
-	depends on CRAMFS=m || MTD=y
+	depends on CRAMFS && CRAMFS <= MTD
 	default y if !CRAMFS_BLOCKDEV
 	help
 	  This option allows the CramFs driver to load data directly from