src/poky:bitbake: fetch2/wget: don't conditionalise --continue

If the target file exists, we pass --continue so that wget will try to
resume the download instead of starting from the beginning.  However if
the file doesn't exist --continue has no effect, so there's no need to
conditionalise the use of the argument.

(Bitbake rev: a5ee50d4d2b2e6c00abe1551382afd9799345dbf)

Signed-off-by: Ross Burton <ross.burtonarm.com>
Signed-off-by: Richard Purdie <richard.purdielinuxfoundation.org>

Author: rossburton