USB: sisusbvga: rename sisusb.c to sisusbvga.c

As it's the only source for the sisusbvga module, there is no need for a
2-steps build.

Cc: Michael Ellerman <[e-mail]>
Cc: Nicholas Piggin <[e-mail]>
Cc: Christophe Leroy <[e-mail]>
Cc: Yoshinori Sato <[e-mail]>
Cc: Rich Felker <[e-mail]>
Cc: Thomas Winischhofer <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Jiri Slaby (SUSE) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/misc/sisusbvga/Makefile

···
 #
 
 obj-$(CONFIG_USB_SISUSBVGA) += sisusbvga.o
-
-sisusbvga-y := sisusb.o