smsc(4): update to mention Microchip
    
    Microchip Technology acquired SMSC in 2012, and all current products
    and datasheets refer to the devices supported by this driver as
    Microchip parts.  Mention SMSC in a parenthetical comment to explain
    the driver's name.
    
    Reviewed by:	imp
    Sponsored by:	The FreeBSD Foundation
    Differential Revision: https://reviews.freebsd.org/D45115
    
    (cherry picked from commit 7ef6ce51742d44a7375ccbaeda4cc64e034c4816)