kbuild: correct initramfs compression comment

Fix the Makefile comment since bzip2 is now supported.
Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

usr/Makefile

@@ -6,7 +6,7 @@ klibcdirs:;
 PHONY += klibcdirs
 
 
-# Gzip, but no bzip2
+# Gzip
 suffix_$(CONFIG_INITRAMFS_COMPRESSION_GZIP)   = .gz
 
 # Bzip2