kconfig: fix typo "mconfig" to "menuconfig" in a comment

# ===========================================================================

# Shared Makefile for the various kconfig executables:

# conf:	  Used for defconfig, oldconfig and related targets

# mconf:  Used for the mconfig target.

# mconf:  Used for the menuconfig target

#         Utilizes the lxdialog package

# qconf:  Used for the xconfig target

#         Based on QT which needs to be installed to compile it