apply-patches: only use first field of line for series file

A series file for quilt has a valid syntax of:

  fixes/autoconf.diff -p1
  fixes/doc-html-local-css.diff -p1
  fixes/gnu-inline.diff -p1

However, with the current way that a series file is handled, it will
error out because the -p1 is tried as a file. This is because in the
for loop that iterates the files, we only look for comment lines. Then
each line is used within a bash for loop which uses spaces a
delimiter. In order to fix this, we should only use the string that
comes before a space in the series file.

Note that the format allows for any arbitrary depth to the -pN field.
But since we'll have only one package with -pN fields, and all will be
-p1, we for now always assume -p1. This will have to be fixed whenever
we get a package with other values.

Signed-off-by: Ryan Barnett <ryanbarnett3@gmail.com>
[yann.morin.1998@free.fr: expand comment about the format of a series
file and how we interpret it]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
CC: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>